Power liftgate drive assembly

ABSTRACT

A powered closure drive mechanism is provided for moving a closure between open and closed positions. An elongated housing extends between first and second ends that are movable in opposite directions toward and away from each other. A rotatable lead screw is disposed longitudinally within the elongated housing. A reversible motor rotates the lead screw in a first direction and a second direction to urge the first and second ends of the housing toward and away from each other. A sensor assembly includes a worm fixed to the lead screw for rotation therewith and a rotatable gear meshingly engaged with the worm. The worm and gear are geared such that the gear rotates less than one revolution in response to the closure moving between the open and closed positions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 11/680,285, filed Feb. 28, 2007, which is a continuation-in-part of International Application No. PCT/CA2006/000254, with an international filing date of Feb. 20, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to power liftgates for motor vehicles, and more particularly, to a power liftgate drive assembly having an absolute position encoder.

2. Description of Related Art

Motor vehicle liftgates or closure panels act to close and seal a rear cargo area of a van, minivan, or sport utility type of motor vehicle. Typically, these closure panels are mounted in a frame located at the rear of the vehicle, usually on a horizontally extending axis provided by a hinge. The liftgate is thus positioned to rotate between a closed position adjacent to the frame and an open position, in which the cargo area of the vehicle is accessible. The liftgate is often very heavy, and because of its mounting, it must be moved against gravity in order to reach the open position. Because of the liftgate's weight, it would be a great burden if a user was required to lift the liftgate into the open position and then manually hold it in place in order to access the vehicle's cargo area.

In order to make it easier to open liftgates, most modern motor vehicles use gas or spring-loaded cylindrical struts to assist the user in opening and holding open liftgates. The struts typically provide enough force to take over the opening of the liftgate after the liftgate has been manually opened to a partially opened position at which the spring force and moment arm provided by the struts are sufficiently to overcome the weight of the liftgate, and to then hold the liftgate in an open position.

Automated power systems to open and close vehicle liftgates are well known in the art. These systems typically use a power actuator to apply a force directly to the liftgate to enable opening and closing thereof. Such automated powered systems act as a direct replacement for the user-supplied force.

With automated power systems to open and close vehicle liftgates it is desirable to provide a position sensor to monitor the position of the liftgate. Most position sensors, however, are limited by the fact that if power is temporarily lost or disconnected, and the liftgate is manually moved, the position sensor cannot detect the position of the liftgate until the position sensor is recalibrated or reset. Therefore, it is desirable to provide a power liftgate drive assembly having a position sensor capable of monitoring the position of the liftgate even after power is temporarily lost or disconnected and the liftgate is manually moved to another position.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a powered closure drive mechanism is provided for moving a closure between an open position and a closed position. The drive mechanism includes an elongated strut assembly extending between first and second ends. A rotatable lead screw is disposed within the strut assembly and a reversible motor turns the lead screw in first and second directions to move the first and second ends toward and away from each other to move the closure between the open and closed positions. A sensor assembly includes a worm fixed to the lead screw for rotation therewith and a gear meshingly engaged with the worm. The worm and gear are geared so that the gear rotates not more than one revolution in response to the closure moving between the open and closed positions.

According to another aspect of the invention, a powered closure drive mechanism is provided for moving a rear liftgate on a motor vehicle between an open position pivoted away from the vehicle and a closed position adjacent the vehicle. The drive mechanism or electro-mechanical strut assembly includes an elongated strut housing extending between the liftgate and the vehicle. A rotatable lead screw is disposed longitudinally within the strut housing and a reversible motor turns the lead screw in a first direction and a second direction to move first and second ends of the strut housing toward and away from each other to move the liftgate between the open and closed positions. A sensor assembly is provided to determine a position of the liftgate between the open and closed positions. The sensor assembly includes a worm fixed to the lead screw for rotation therewith, a gear meshingly engaged with the worm, a two-pole magnet, and a sensor. The worm and gear are geared so that the gear rotates not more than one revolution in response to the liftgate moving between the open and closed positions. The magnet has a magnetic field and is mounted to the gear for rotation therewith. The sensor senses the magnetic field and generates an output signal to determine a rotational position of the magnet which corresponds to the position of the liftgate.

According to yet another aspect of the invention, an absolute position encoder is provided for determining a position of a rear liftgate on a motor vehicle that is movable between an open position and a closed position by a strut assembly. The encoder includes a two-pole magnet and a sensor. The magnet has a magnetic field and is operatively coupled to the strut assembly to rotate not more than one revolution in response to the liftgate moving between the open position and the closed position. The sensor is adapted to be mounted to the strut assembly and senses the magnetic field of the magnet. The sensor outputs a signal in response to sensing the magnetic field to determine a rotational position of the magnet which corresponds to the position of the liftgate between the open and closed positions.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a motor vehicle with a rear liftgate in an open position;

FIG. 2 is a side view of the motor vehicle with the rear liftgate in a closed position;

FIG. 3 is a cross-sectional view of a liftgate strut assembly according to the invention;

FIG. 4 is a fragmentary, enlarged cross-sectional view of the liftgate strut assembly;

FIG. 5 is a partially cut-away perspective view of a sensor assembly; and

FIG. 6 is a cross-sectional end view of the sensor assembly.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described below particularly with respect to its application in rear liftgates of motor vehicles. Those skilled in the art will, however, realize that the present invention may be applied to other types of vehicle closures and also to closures that are not mounted on vehicles. For example, the present invention may find application in trunk lids for motor vehicles, panels covers for light trucks, train doors, bus doors, and household closures such as windows and doors. In addition, it is contemplated that the present invention has utility for other automotive applications such as steering wheel position sensing, gas pedal position sensing, transmission gearbox encoder, headlight position control, and power seat position sensing.

Referring now more particularly to the drawings, there is shown in FIG. 1 a motor vehicle, generally shown at 10, with a vehicle body or frame 12 which defines an opening 14 at a rear end thereof. A liftgate or door 16 (or more generally referred to as a “closure”) is adapted to fit within the opening 14. The weight of the closure 16 biases it towards a closed position within the opening 14, as shown in FIG. 1.

A hinge assembly 18 is connected between an upper portion 20 of the vehicle body 12 and an upper portion 22 of the closure 16, pivotally mounting the closure 16 to the vehicle body 12. The hinge assembly 18 provides a generally horizontally extending axis 24 for pivotal movement of the closure 16 between the closed position, adjacent the vehicle body 12, as shown in FIG. 2, and an open position, pivoted away from the vehicle body 12 such that the cargo area of the vehicle 10 is accessible, as shown in FIG. 1.

A latch assembly 26 having cooperating parts mounted on the closure 16 and the vehicle body 12 is also shown in FIG. 1. The latch assembly 26 is provided for releasably locking the closure 16 in the closed position. The latch assembly 26 includes a latch 28 disposed within a lower portion 30 of the closure 16 and a complimentary latch striker 32 disposed within a lower portion 34 of the vehicle body 12.

A powered closure drive mechanism, generally shown at 36, is provided for opening and closing the closure 16. More particularly, the powered closure drive mechanism 36 is disclosed as a pair of electro-mechanical strut assemblies 38. Each strut assembly 38 extends between a first end 40 and a second end 42, the first 40 and second 42 ends being movable in opposite directions toward and away from each other. In the illustrated embodiment, one strut assembly 38 is mounted on each side of the vehicle 10, extending between the closure 16 and the vehicle body 12. It is appreciated by one of skill in the art that a single strut assembly 38 connected between the closure 16 and the vehicle body 12 will provide the necessary function of opening and closing the closure 16. The first end 40 of the strut assembly 38 is operatively coupled to the vehicle body 12, adjacent the upper portion 20 thereof. The second end 42 of the strut assembly 38 is pivotally coupled to an edge 44 of the closure 16, between the upper 22 and lower 30 portions thereof.

One strut assembly 38 is shown in detail in FIG. 3. The strut assembly 38 includes a housing 46 enclosing the various components of the strut assembly 38. Internally, a motor 48 is disposed toward the second end 42 of the strut assembly 38. The motor 48 is electrically connected to an electric energy source (not shown). It is contemplated that the motor 48 operates using electric energy that is standard in a motor vehicle protocol. The motor 48 is bi-directional allowing for rotation of a drive shaft 50 in two directions. The drive shaft 50 extends axially within the strut assembly 38 and is operatively coupled to a gearbox 52. The gearbox 52 is disposed adjacent the motor 48.

The gearbox 52 includes an output shaft 54 that is driven by the drive shaft 50 of the motor 48 and extends coaxially therewith. The output shaft 54 of the gearbox 52 is operatively coupled to a lead screw 56 by a clutch assembly 58, disposed adjacent the gearbox 52. The clutch assembly 58 rotates the lead screw 56 in response to a rotational input from the output shaft 54 of the gearbox 52. The clutch assembly 58 is an overload-type clutch in that it slips at a predetermined torque, but not below the predetermined torque. The clutch assembly 58 allows selective manual movement of the closure 16 between the open and closed positions.

The lead screw 56 extends coaxially with the output shaft 54 of the gearbox 52 between a first end 60 disposed within the clutch assembly 58 and a second end 62 disposed at the first end 40 of the strut assembly 38. A first portion 66 of the lead screw 56 adjacent the first end 60 is unthreaded while a remaining second portion 68 is threaded. A support nut 70 threadingly engages the threaded second portion 68 of the lead screw 56. As the lead screw 56 rotates, the support nut 70 is driven linearly along the lead screw 56 in either a first direction or a second direction depending on the direction of rotation of the lead screw 56. Linear travel of the support nut 70 along the lead screw 56 causes the first end 40 of the strut assembly 38 to move towards and away from the second end 42, thereby causing the closure 16 to pivot between the open and closed positions. In one embodiment of the invention, the lead screw 56 is rotated approximately ten (10) revolutions to drive the support nut 70 between a first location, which corresponds to the closure 16 being in the closed position, and a second location, which corresponds to the closure 16 being in the open position.

It is necessary to monitor exactly where the closure 16 is within its range of travel between the open and closed positions. To accomplish this, the strut assembly 38 also includes a sensor assembly 72 disposed between the clutch assembly 58 and the support nut 70. The lead screw 56 extends through the sensor assembly 72. The sensor assembly 72 includes a sensor housing 74 that defines an internal compartment 76. A worm 78 and gear 80 are disposed within the internal compartment 76 and oriented generally orthogonal to each other. The unthreaded first portion 66 of the lead screw 56 extends axially through the worm 78 and the worm 78 is keyed or fixed to the lead screw 56 such that it rotates therewith. The gear 80 is mounted in meshing engagement with the worm 78 such that rotation of the worm 78 causes the gear 80 to rotate. The gear ratio between the worm 78 and the gear 80 is approximately 10:1 such that the gear 80 rotates not more than one (1) revolution for every ten (10) revolutions of the worm 78, which corresponds to full travel of the closure 16 between the open and closed positions or alternatively between the closed and open positions.

A diametrically charged or two-pole magnet 82 is generally disc-shaped and is fixedly secured to a distal end of the gear 80 and rotates therewith. Therefore, the magnet 82 rotates not more than one (1) revolution for full travel of the closure 16. The magnet 82 has a north pole and a south pole which create a magnetic field. A board 84 with a chip 86 mounted thereon is fixedly secured to the sensor housing 74 adjacent the magnet 82. The chip 86 includes at least one sensor mounted therein for sensing the magnetic field of the magnet 82 in order to resolve its rotational position. The chip 86 then outputs the rotational position of the magnet 82 to a controller 88 located within the vehicle. The controller 88 is electrically connected to the chip 86 and to the motor 48. The chip 86 may output the rotational position of the magnet 82 in any number of suitable ways. For example, the chip 86 may output a linear analog signal that is proportional to position wherein approximately zero volts corresponds to the closed position of the closure 16 and approximately five volts corresponds to the open position of the closure 16. One benefit of this powered closure drive mechanism 36 is that the chip 86 can always determine the absolute rotational position of the magnet 82 based on its magnetic field, even after a power disconnect during which the closure 16 is manually moved to a new position. The chip 86 is any suitable chip for sensing the magnetic field of the magnet 82 and outputting the rotational position of the magnet 82, for example, the AS5040-10 bit Programmable Rotary Encoder manufactured by Austria Micro Systems AC.

To initially calibrate the chip 86, the magnet 82 needs to be set to a predetermined position relative to the lead screw 56, so that approximately zero volts will correspond to the closed position of the closure 16 and approximately five volts will correspond to the open position of the closure 16. Alternatively, the system can be assembled without paying attention to the alignment of the magnet 82 relative to the lead screw 56. In this situation, with the closure 16 in the closed position the zero position is programmed into the chip 86.

It is appreciated that the lead screw threads can be selected such that any number of revolutions of the lead screw 56 is required to drive the support nut 70 between the first and second locations without varying from the scope of the invention. However, in order to accommodate a different number of revolutions of the lead screw 56, the worm 78 and gear 80 must be selected such that the magnet 82 rotates not more than one (1) revolution for full travel of the closure 16.

The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described. 

1. A powered closure drive mechanism for moving a closure between an open position and a closed position, said powered closure drive mechanism comprising: an elongated housing extending between first and second ends, said first and second ends being movable in opposite directions toward and away from each other; a rotatable lead screw disposed longitudinally within said elongated housing; a reversible motor operatively coupled to said lead screw for rotation of said lead screw in a first direction and a second direction thereby urging said first and second ends of said elongated housing toward and away from each other; and a sensor assembly including a worm fixed to said lead screw for rotation therewith, and a rotatable gear meshingly engaged with said worm, wherein said worm and gear are geared such that said gear rotates not more than one revolution in response to the closure moving between the open and closed positions.
 2. A powered closure drive mechanism as set forth in claim 1 further including a nut threadingly engaging said lead screw and moving linearly therealong in response to rotation of said lead screw in either said first or second direction thereby urging said first and second ends of said elongated housing toward and away from each other.
 3. A powered closure drive mechanism as set forth in claim 2 whereby linear movement of said nut in a first linear direction urges said first and second ends of said elongated housing away from each other to move the closure to the open position and whereby linear movement of said nut in a second linear direction allows the weight of the closure to move the closure to the closed position.
 4. A powered closure drive mechanism as set forth in claim 3 wherein said gear is disposed generally orthogonal to said worm.
 5. A powered closure drive mechanism as set forth in claim 4 further including a two-pole magnet fixedly secured to said gear for rotation therewith, said magnet generating a magnetic field, and a sensor mounted adjacent said magnet for sensing said magnetic field and resolving a rotational position of said magnet wherein said rotational position of said magnet corresponds to a position of the closure between the open and closed positions.
 6. A powered closure drive mechanism as set forth in claim 5 further including a controller operatively connected with said motor and said sensor, said controller controlling said motor to move the closure between the open and closed positions based upon said rotational position of said magnet.
 7. A powered closure drive mechanism as set forth in claim 6 further including a sensor assembly housing, wherein said rotatable gear is rotatably coupled to said sensor assembly housing and meshingly engaged with said worm.
 8. A powered closure drive mechanism as set forth in claim 7 further including a gearbox operatively coupled to said motor for transmitting an input rotation from said motor to an output shaft.
 9. A powered closure drive mechanism as set forth in claim 8 further including a clutch assembly operatively coupling said output shaft of said gearbox and said lead screw for transmitting rotation of said output shaft to said lead screw.
 10. A powered closure drive mechanism as set forth in claim 9 wherein said motor is disposed toward said second end of said elongated housing, said gearbox is disposed adjacent said motor, said clutch assembly is disposed adjacent said gearbox, said sensor assembly is disposed adjacent said clutch assembly, and wherein said lead screw extends through said sensor assembly housing.
 11. A powered closure drive mechanism as set forth in claim 10 wherein said lead screw extends between a first end operatively coupled to said clutch assembly and a second end disposed toward said first end of said elongated housing.
 12. A powered closure drive mechanism as set forth in claim 11 wherein said lead screw includes a first unthreaded portion adjacent said first end of said lead screw and a second threaded portion, said worm fixed to said first unthreaded portion and said nut threadingly engaging said second threaded portion.
 13. A powered closure for a motor vehicle having an opening, said powered closure comprising: a rear liftgate pivotally coupled to the motor vehicle for movement between an open position pivoted away from the motor vehicle uncovering the opening and a closed position adjacent the motor vehicle covering the opening; at least one strut assembly extending between a first end operatively coupled to the motor vehicle and a second end operatively coupled to said rear liftgate, wherein said first and second ends are movable in opposite directions toward and away from each other to move said rear liftgate between said open and closed positions; and an absolute position encoder including a two-pole magnet and a sensor, said magnet having a magnetic field and operatively coupled to said at least one strut assembly to rotate not more than one revolution in response to said rear liftgate moving between said open and closed positions, said sensor mounted to said at least one strut assembly for sensing said magnetic field of said magnet and generating an output signal to determine a rotational position of said magnet which corresponds to the position of said rear liftgate between said open and closed positions.
 14. A powered closure as set forth in claim 13 wherein said strut assembly includes an elongated housing extending between first and second ends, said first and second ends being movable in opposite directions toward and away from each other, a rotatable lead screw disposed longitudinally within said elongated housing, and a reversible motor operatively coupled to said lead screw for rotation of said lead screw in a first direction and a second direction thereby urging said first and second ends of said elongated housing toward and away from each other.
 15. A powered closure as set forth in claim 14 further including a worm fixedly secured to said lead screw for rotation therewith, and a rotatable gear meshingly engaged with said worm, wherein said magnet is fixedly secured to said gear, and wherein said worm and gear are geared such that said gear rotates not more than one revolution in response to said rear liftgate moving between said open and closed positions.
 16. A powered closure as set forth in claim 15 wherein said gear is disposed generally orthogonal to said worm.
 17. An absolute position encoder for determining a position of a rear liftgate on a motor vehicle movable between open and closed positions by a strut assembly, said absolute position encoder comprising: a two-pole magnet having a magnetic field, said magnet operatively coupled to the strut assembly and geared to rotate not more than one revolution in response to the rear liftgate moving between the open position and the closed position; and a sensor adapted to be mounted to the strut assembly, said sensor sensing said magnetic field of said magnet and generating an output signal to determine a rotational position of said magnet which corresponds to the position of the rear liftgate between the open and closed positions. 